Modelling light for projection
A performance/installation/space that is viewed from a single point (for example, when the viewer is sitting down), offers an opportunity to create virtual threedimensional spaces on the surfaces of existing physical structures. A very simplified example would be a projection screen projected with a hole into a projected space beyond the screens physical space

A screen in a room showing similar virtual rooms in the same perspective.
However, this idea of playing with perspective in order to continue space seems very limiting, mainly because of the very limited field of view.
Another way of extending physical space into virtual, could be the use of virtual light, for example light coming from beyond the physical walls. With virtual light it could be suggested, that there are other spaces beond the one we can see, and other events taking place.
Virtual light with video projection
Virtual light enables various interesting possibilities. In a theatre play, mixing virtual light with conventional light sources, could generate some new esthetics and ways to manipulate time and space. For example, a timelapse of scenic elements shadows moving across stage. The basic idea here would be mixing reality seamlessly, so that the media or tool used to create the content could not be named.

